Such plants and processes are known. In Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, Vol. 13, page 115, this process is described in principle as “trickle-bed hydrogenation”. Under elevated pressure and at elevated temperature, the fatty acid ester to be converted here is mixed in liquid form with gaseous hydrogen stoichiometrically added in excess to obtain an educt mixture. The educt mixture is passed over a catalyst fixed bed, which also can be referred to as trickle bed, wherein the educt mixture is converted into a product mixture consisting of fatty alcohol, hydrogen and, depending on the fatty acid ester used, also of further alcohols. The product mixture is cooled to a temperature in the range from 40 to 80° C., preferably 60 to 80° C. Then, the hydrogen and highly volatile components are separated from the product mixture. The liquid fatty alcohol is discharged from the plant as product for the further use. The hydrogen is recirculated to the beginning of the process, where it is combined with fresh hydrogen and reused for forming the educt mixture.
For carrying out the catalytic conversion, the educt mixture is charged to the catalyst fixed bed (trickle bed) with a temperature in the range from 150 to 250° C., preferably 180 to 250° C. The hydrogenation proceeds exothermally, wherein a too strong rise of the temperature of the educt/product mixture must be avoided, in order to keep the formation of undesired by-products as low as possible.
In the German patent specification DE 198 43 798 C2 a process variant therefore is proposed, in which quench hydrogen is introduced into the catalyst fixed bed to limit the rise in temperature. The quench hydrogen is obtained by branching off one part of the cooled hydrogen separated from the product mixture as “quench hydrogen”. The remaining hydrogen, mixed with fresh hydrogen, is recirculated to the beginning of the process as cycle hydrogen and used to form the educt mixture. It also is proposed there to split up the catalyst fixed bed and arrange it in two series-connected reactors and in the process likewise feed quench hydrogen into the transfer conduit between the reactors for the educt/product mixture.
In these plant and process concepts it is disadvantageous that the plant must be shut down to exchange the catalyst whose effect decreases after a certain operating time. It furthermore is disadvantageous that the effectiveness of the bottommost part of the catalyst bed cannot fully be utilized.